1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor device packages, and more particularly to a method for manufacturing digital micro-mirror device (DMD) packages.
2. Description of the Related Arts
In order to keep pace with the development of personal computers, a display has been developed from a cathode-ray tube type display into a liquid crystal display or a mirror type display. Especially, with the increasing demand for digital broadcasting appliances, a digital light processing (DLP) technology for high resolution becomes more and more important. A DMD, which is an essential component for the DLP technology, requires significant expertise in the manufacturing process for mirrors so that high reliability and low cost in the manufacturing process can be obtained.
The DMD process involves driving the mirrors, and thus the proper driving of mirrors is very important. Further, moisture and dust within the packages affect the picture quality or resolution of the DMD as well as its reliability or durability. Therefore, during the fabrication of the DMD packages, the DMD packages themselves need to be protected from moisture and dust.
FIG. 1 is a plan view showing a conventional semiconductor chip 12 for the DMD, and FIG. 2 is a cross-sectional view showing a DMD package 100 containing the semiconductor chip 12 of FIG. 1. With reference to FIG. 1 and FIG. 2, the semiconductor chip 12 is attached to an upper surface 21 of a base substrate 20 by interposing an Ag-epoxy adhesive 30 therebetween. The semiconductor chip 12 and the base substrate 20 are electrically interconnected to each other with one or more bonding wires 40. In order to protect the semiconductor chip 12 from external environmental stresses, a metal sealing ring 24 with a predetermined height is provided at the periphery of the upper surface 21 of the base substrate 20.
The components, including the semiconductor chip 12, are hermetically sealed up with a window lid 50. A heat sink stud 60 is attached to the lower surface 23 of the base substrate 20. The window lid 50 comprises a metal lid frame 52 contacting the metal sealing ring 24, and a window 54. A reflectance coating film 56 is applied to the lower surface of the window 54 along the periphery thereof. The metal sealing ring 24 and the base substrate 20 form a cavity 29, and a moisture getter (absorbent) 58 is attached to the lower surface of the metal lid frame 52 of the window lid 50 within the cavity 29. External terminals (not shown) are formed on the lower surface 23 of the base substrate 20.
A plurality of mirrors 16 (only a typical one of which is depicted in FIG. 2) are formed on the active surface of the semiconductor chip 12 at the center thereof, and one or more electrode pads 14 are formed on the active surface at the periphery thereof for interconnection via the one or more bonding wires 40.
FIG. 3 is a flow chart 90 describing a manufacturing process of the conventional DMD package 100. Each step of the manufacturing process is described briefly below.
A wafer comprising a plurality of the semiconductor chips 12 is prepared (step 71). Herein, a photoresist film is formed on the upper surface of the wafer in the predetermined portion. The photoresist film prevents damage to the mirrors 16 from the external environment by covering the mirrors 16. The photoresist film is not formed on the electrode pads 14.
Prior to wafer-breaking, the wafer is half-cut (step 72). The photoresist film on the upper surface of the wafer is removed (step 73), and to shield the mirrors 16 from dust or moisture, a first anti-sticking film is formed thereon (step 74). The wafer is broken and separated into individual semiconductor chips 12 (step 75). A breaking means in a dome shape is brought into contact with to the back surface of the wafer and urged upwardly. As a result, the half-cut wafer is broken into a plurality of individual semiconductor chips 12.
The silicon particles generated during the wafer-breaking step are then removed (step 76).
The semiconductor chip 12 is attached to the upper surface 21 of the base substrate 20 by the Ag-epoxy adhesive 30 (step 77), and the Ag-epoxy adhesive 30 is cured (step 78). The semiconductor chip 12 is electrically interconnected to the base substrate 20 with the bonding wires 40 (step 79).
The organic compounds remaining on the upper surface 21 of the base substrate 20, the semiconductor chip 12 on the surface 21, and the bonding wires 40 are removed (step 80). A second anti-sticking film is formed thereon (step 81).
The metal sealing ring 24 is mounted on the upper surface 21 of the base substrate 20, and the components are hermetically sealed by the window lid 50 having the moisture getter 58 attached thereon (step 82).
The heat sink stud 60 is attached to the lower surface 23 of the base substrate 20 (step 83). The DMD package 100 is thus complete.
The above-described method for manufacturing the conventional DMD packages has several problems as follows;
The manufacturing process is very complicated. The major reason is that the manufacturing process for the conventional DMD package employs the wafer-breaking method for separating the wafer into individual semiconductor chips 12. Since the wafer-breaking method comprises a first step of half-cutting the wafer and a second step of breaking the wafer, compared to the full-cutting method, which completely cuts the wafer at once, this method further involves an additional step, i.e. the wafer-breaking step.
Even if the fall-cutting method is employed to prevent this drawback, another problem occurs in the step of removing the photoresist after separating the wafer into the semiconductor chips by the full-cutting method. Conventionally, the wafer comprising separated semiconductor chips has the adhesive tape on its back surface. In the photoresist-removing step after the wafer-cutting step, the adhesive from the adhesive tape and the photoresist are unnecessarily removed together. Thus, the individual semiconductor chips can be undesirably detached from the adhesive tape. Therefore, the conventional manufacturing process normally cannot employ the fall-cutting method.
The mirrors within the semiconductor chip 12 can be easily damaged by the silicon particles generated in the wafer-breaking step. The silicon particles positioned between the mirrors 16 cannot be properly removed by the washing step. Since the wafer-breaking step is carried out after the step of removing the photoresist, damage to the mirrors 16 by the silicon particles commonly occurs.
Since the Ag-epoxy adhesive is used to attach the semiconductor chip 12 to the base substrate 20, moisture enters the package due to the hygroscopicity of the Ag-epoxy. Further, an exhaust gas generated during the curing of the Ag-epoxy adhesive contaminates the mirrors 16 on the active surface of the semiconductor chip 12. Therefore, it is preferable to use solder as the adhesive means. However, with the use of the solder, damage such as the burning of the first anti-sticking film or the deformation of the mirrors can occur. In other words, to attach the semiconductor chip to the base substrate, the solder must be melted at a temperature of 150xc2x0 C. or more. Such a high temperature causes the burning of the first anti-sticking film or the deformation of the mirrors 16 in the semiconductor chip 12.
Accordingly, an object of the present invention is to simplify the manufacturing process of the DMD packages.
Another object of the present invention is to prevent failures generated in the sequence of steps including first half-cutting and second full-cutting the wafer.
Still another object of the present invention is to prevent failures due to the use of the Ag-epoxy adhesive.
In order to achieve the foregoing and other objects, a method for manufacturing digital micro-mirror device (DMD) packages comprises preparing a wafer including a plurality of DMD semiconductor chips, each chip having a plurality of mirrors formed on the center of an active surface, a plurality of electrode pads formed on the edges of the active surface, and a photoresist for protecting the mirrors. The method further comprises forming a metallic layer on a back surface of the wafer, said metallic layer being made of a metal having a low melting point. It further comprises separating the wafer into the individual semiconductor chips. It also comprises attaching each semiconductor chip to an upper surface of a base substrate with an adhesive made of a metal having a low melting point. The method then comprises the steps of interconnecting the electrode pads of the semiconductor chip to the base substrate with a bonding wire, removing the photoresist from the semiconductor chips, and forming an anti-sticking film on the active surface of the semiconductor chip for protecting the semiconductor chips from dust and moisture. Finally, the method comprises hermetically sealing the semiconductor chip and the bonding wires on the upper surface of the base substrate by using a window lid.
It is preferable that the metallic layer is made of a metal having a low melting point selected from the group consisting of Va, Au, Ni, Ag, Cu, Al, Pb, Sn, Sb, Pd and metallic compounds thereof.
The step of forming a metallic layer comprises lapping the back surface of the wafer and forming on the back surface a metallic layer made of a metal having a low melting point.
Solder is preferably used as the metal adhesive having a low melting point.
After the step of hermetically sealing the semiconductor chip and the bonding wires, the manufacturing method of the DMD packages further comprises attaching a heat sink stud to the lower surface of the base substrate. Further, it is preferable that the step of hermetically sealing the semiconductor chip and the bonding wires is carried out at a temperature which is no higher than the temperature of the step of attaching the semiconductor chip to the base substrate.